The present invention relates to an on-board type power module.
Recently, in developing electronic equipment that meets demand toward miniaturization in the market, measures for heat dissipation of heating components mounted on a board at high density (ex. electronic components such as semiconductor device) have increasingly become important. Especially in a power module, since insufficient heat dissipation of components can impair reliability of the components, measures for heat dissipation are extremely important in order to suppress temperature rise due to heat generation of power conversion devices mounted at high density and the like.
As measures for heat dissipation, prior art power modules have adopted a forced air-cooling system with fan or a heat transfer cooling system wherein a high thermal conductive heat sink is pressed onto heating components, thereby to efficiently transfer heat from the heating components to the heat sink for cooling them.
Various electronic components requiring heat dissipation such as MOSFET (MOS (metal-oxide semiconductor) field-effect transistor), transformer, choke, IC for power supply circuit and the like are mounted on a circuit board of a power module. These electronic components vary in shape and height, thereby to generate difference in level among them. There are variations in heights of the components themselves as well as mounted heights of the components on the circuit board. For that reason, even if a heat sink is pressed onto plural heating components, it is difficult to bring all components into coherent with the heat sink evenly. Therefore, it is necessary to accommodate difference in level and height among the heating components and bring the electronic components requiring heat dissipation into coherent with the heat sink so as to ensure heat transfer between them.
In order to solve this problem, Patent Publication No. 2536657 describes a prior art electronic apparatus that comprises a heat sink having depressed portions for accommodating components mounted on a multi-layer board depending on positions and heights of the components. The prior art electronic apparatus disclosed in Patent Publication No. 2536657 will be described below. FIG. 19 is a sectional view of the circuit board disclosed in the above-mentioned Patent Publication.
In FIG. 19, conductors 21a are provided with a circuit board 21 in a predetermined pattern. A resistance 22 as an electronic component with high heating value, a cement resistance 23 with especially high heating value, an electrolytic capacitor 26 as an electronic component with low heating value, a power module 27 with high heating value and the like are fixed to the circuit board 21 by soldering 25. A reference numeral 20 denotes a base made of aluminum die cast. The base 20 has depressed portions 20a for inserting the components 22, 23, 26, 27, respectively, depending on position, height and shape thereof so as to make space between the base 20 and each component substantially same.
A copper cover 28 having the same shape as outline of the cement resistance 23 lies between the cement resistance 23 and the depressed portion 20a. A high thermal conductive resin 29 is filled in each space (depressed portion 20a) between the resistance 22, cement resistance 23 and power module 27, respectively, all of which have a high heating value, and the base 20. A heat-insulating resin 30 is filled in the space (depressed portion 20a) between the electrolytic capacitor 26 with low heating value and the base 20.
A reference numeral 31 denotes a terminal part of each component, a reference numeral 32 denotes a nut for electrically bonding the terminal part 31 to the conductor 21a of the circuit board 21, a reference numeral 33 denotes a fastening screw for electrically connecting the terminal part 31 to the conductor 21a of the circuit board 21, and a reference numeral 34 denotes a holding member for holding the circuit board 21 on the base 20.
In other words, the prior art electronic apparatus enables efficient heat transfer, since both the tall and short components with high heating value are adhered to the heat sink evenly.
In the prior art example, however, there causes a problem of complicating configuration of the heat sink. The heat sink must be designed so as to have convexocancave that correspond to any difference in level ranging from large to minute differences in response to the components of various heights that are mounted on the circuit board. A mold for the heat sink with complicated shape is expensive. In the case of highly complicated shaped heat sink, aluminum die cast drawn from the mold needs to be processed thereafter. Thus, it is impossible to design the heat sink until the pattern of the circuit board and components attached thereto have been determined, and production of the mold for the complicated heat sink takes a long time, thereby to cause delay in going on the market. Moreover, once the shape of heat sink has been established, it becomes difficult to change electronic components on the multi-layer board or their positions. These problems have resulted in prolongation of development period and increase in production cost.
An object of the present invention is to provide a power module that has structural characteristics including good heat dissipation, high thermal resistance reliability, low-cost and high productivity.
Another object of the present invention is to provide a power module that efficiently takes heat generated from components of various heights, which are mounted on the circuit board, by use of a multipurpose heat sink or a simple-shaped heat sink.
Another object of the present invention is to provide a lightweight power module due to miniaturization and weight saving of heat dissipation member.